Retirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligation	$ 12.5	$ 8.9
Expected return on assets	(14.4)	(15.7)
Amortization of net losses (gains)	0.0	7.7
Retirement benefits (income) expense	(1.9)	0.9
Postretirement Medical and Life Insurance Benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligation	0.2	0.1
Expected return on assets	0.0	0.0
Amortization of net losses (gains)	(0.7)	(0.7)
Retirement benefits (income) expense	$ (0.5)	$ (0.6)